The embodiments of the present invention pertain to the domain of communication networks, and more particularly to the distribution of time between two Synchronous Ethernet (SyncE) domains interconnected by a Synchronous Optical Networking/Synchronous Digital Hierarchy (SONET/SDH) domain. This is because the SONET/SDH and SyncE domains are compatible from the viewpoint of the physical distribution of a synchronization frequency as depicted in FIG. 1, wherein Synchronized Ethernet (syncE) nodes E (FIG. 1b) or hybrid nodes H (FIG. 1c), meaning those that have both SONET/SDH and SyncE, are inserted into a synchronization chain comprising SONET/SDH nodes S and synchronization units (Synchronization Supply Unit) SSU.
The synchronization status is therefore distributed by Ethernet Synchronization Messaging Channel messages (ESMC) that contain Type Length Value (TLV) structures as specified in protocol 802.3 of the Institute of Electrical and Electronic Engineers (IEEE 802.3).
At present, only one of those TLV structures is standardized by the International Telecommunications Union (ITU-T); this is the TLV field indicating the synchronization signal's quality level (QL-TLV) in order to maintain compatibility with SONET/SDH.
Proposals to add TLV structures have, however, been proposed within UIT-T in order to optimize the use of those ESMC messages, and particularly to introduce a TLV structure that comprises a timestamp value so as to distribute time through a SyncE domain.
In the configuration described in FIG. 2 in which two SyncE domains 1 are interconnected by one SONET/SDH domain 3, the additional TLV structures 7, if any (meaning those besides the QL-TLV structure 9) are filtered within the SyncE-SONET/SDH interface. This is because this information is not defined in the SONET/SDH header, and there is no longer any way to extend the format of those headers without deeply impacting (i.e. hardware changes) the large amount of SONET/SDH equipment already deployed on the premises.
There is therefore a need to propose a method that would make it possible to distribute time between two ESMC domains interconnected by a SDH/SONET domain.